Fatigue Strength of Sintered and Heat Treated Compacts made from Composite-type Alloyed Steel Powder

Compacts made from a composite-type alloyed steel powder with 2% Ni and 1% Mo attained high endurance limits of rolling bending and contact fatigue strengths of 460MPa and 2560MPa, respectively, after case hardening. These endurance limits were much higher than those of a conventional 4%Ni-0.5%Mo-1.5%Cu alloyed steel powder, which were 410MPa and 2430MPa, respectively. When double pressed, double sintered and bright quenched, compacts made from the 2%Ni-1%Mo alloyed steel powder showed endurance limits of rotating bending strength of 390MPa and contact fatigue strength of 2710MPa, both higher than those of the compacts made from the conventional alloyed steel powder, which were 350MPa and 233(MPa, respectively. The results of micro-X-ray analysis indicated the decrease in the amount of austenite phase near the fatigue-fractured surface. The improvement of fatigue strength was therefore attributed to the strain-induced martensitic transformation of Ni-rich austenite.